The intensive nature of modern animal husbandry has changed the environmental conditions, so that protection against diseases, especially those caused by secondary pathogenic organisms, becomes an increasing concern. Production inefficiencies become more and more important. Because of their complex nature, many associated problems cannot be solved by farmers alone. With the introduction of information technology in the form of expert systems, new possibilities emerge for maximal productivity and animal health. Expert systems are a new type of computer programmes which are able to handle problems in limited domains at an expert level, using expert knowledge and reasoning processes, within strictly defined problem limits. Expert systems as they presently exist have the following components: a knowledge base (rule- and data-base), inference engine (deductive mechanism), user-interface (explanatory facilities, etc.). The application of knowledge engineering in animal husbandry may result in improvements in the general health and productivity of the herd and the financial returns of the farm, derived from the improved managerial control. At the same time the use of knowledge engineering may lead to greater understanding of the various epidemiological factors that influence farm results, either positively or negatively.